Justification:
This species is abundant throughout the Indo-Pacific. Although it is intensively collected for the aquarium trade, it is not thought to be contributing to any widespread population decline. It is listed as Least Concern. More research is needed on sustainable harvest levels and the impact of collection on this species.

This species is found in the Indo-Pacific from southern and eastern Africa and the Red Sea to the Tuamotus in the south Pacific, and from southern Japan to the southern Great Barrier Reef and south-western Australia.

It is common in the southern coral areas of the Ryukyu Islands and Ogasawara Islands (Kataoka et al. 1970), on the inshore rocky reefs, whereas it does not live on the sand or pebble areas (Kuwamura 1981). The populations increased in summer and autumn, but decreased in winter, sometimes nearly zero. About 0.9 individuals per 100 m2 have been recorded at rocky reefs at Shirahama (Kuwamura 1981).

It is common in the Capricorn/ Bunker Group, One Tree and Heron Islands and Wistari Reef, Fairfax, Fitzroy, Llewellyn and Musgrave Islands on the Great Barrier Reef, with 1.77 recruits per 100m2 (Eckert 1984).

In Australia, it was found to be one of the most abundant labrids at Lizard Island, GBR (three individuals per 150 m2) and occurred in similar densities in all habitat zones (Green 1996).

In Hong Kong, it is common in shallow areas of boulders and coral areas, but never abundant (Sadovy and Cornish 2000).

In Fiji, a total of 475 individuals were observed in various UVC surveys with body sizes of 4-17 cm TL (M. Kulbicki pers. comm. 2008).

In New Caledonia, a total of 1,407 individuals were observed in various UVC surveys with body sizes of 3-22 cm TL. In 31 stations, a total of 58 individuals were caught with a total weight of 242.1 g (M. Kulbicki pers. comm. 2008).

In French Polynesia, a total of 568 individuals were observed in various UVC surveys with body sizes of 4-12 cm TL (M. Kulbicki pers. comm. 2008)

In Tonga, a total of 205 individuals were observed in various UVC surveys with body sizes of 3-11 cm TL (M. Kulbicki pers. comm. 2008).

Mean density was 1.5 fish per 100 m2 on coral reefs of the Adang-ra Wi Islands in the Adaman Sea (Satapoomin undated).

It is common at Enewetak Atoll, Marshall Islands (Colin and Bell 1991), Solomon Islands (Allen 2006) and in the Red Sea (Richard and Field 1998).

This species inhabits coral rich areas and subtidal reef flats to seaward reefs to depths of at least 40 m. It is widely reported to be a monandric hermaphrodite but further confirmed to display bi-directional sex-change, exhibits socially controlled sex reversal and lives in single-male, multiple female social groups (Kuwamura 1984, Sadovy and Cornish 2000, Kuwamura et al. 2002, Sadovy de Mitcheson and Liu 2008). Males exhibit territoriality and the largest, oldest individual is a male which dominates all the females in the group (Robertson 1972, Nakashima et al. 2000).

It feeds on crustaceans ectoparasites and mucus of fishes which gather at specific cleaning ‘stations’ for attention (Pott 1973). Males and females are the same in colour, juveniles are black with a single blue stripe running from snout to the upper part of caudal fin.

It is active in daytime and is reported to be able to produce a protective mucous cocoon at night. Seasonal fluctuation of the activity rate has been observed with almost all individuals always active during late spring and early summer (Kuwamura 1981).

In Japan, spawning occurred within 4-5 months of the year, from late May to early September. Larvae of about 1.8 mm in total length hatch at 30 hours after spawning (Kuwamura 1981).

This species is monochromatic, spawns in harem. Spawning ascent distance was about three m with rapid ascending speed. Spawning activities were seen in March, May, June and November at Enewetak Atoll, Marshall Islands (Colin and Bell 1991). The size of eggs is approximately 0.64 mm and spherical in shape. Eggs contained multiple oil globules

Maximum size of species has been recorded at 22 cm (TL) in New Caledonia and maturity is reached at a size of about six cm TL (Kuwamura 1981, M. Kulbicki pers. comm.). All of the larger adults have an almost completely developed ventroanterior hook in the caudal fin. Maximum lifespan is estimated to be four years (Allsop and West 2003) and minimum population doubling time is approximately 1.4-4.4 years (Froese and Pauly 2008).

It shows cleaning behaviour, which only occurs during the day and particularly in the early morning (Grutter 1996). In captivity it is affected by abundance and size-frequency distribution of the monogenean parasites on the host of fishes, which was more pronounced on larger fish than on small fish (Grutter et al. 2002). It spends 60 to 154 more times cleaning larger fishes (> 12.5 cm SL) than medium (9.5 to 12.5 cm SL) or small sized fish (< 9.5 cm SL). In the Great Barrier Reef, it was found to spend 256 +/- min per day cleaning 2297 +/- 83 fish (Grutter 1996) from over 132 species (Grutter and Poulin 1998). In New Caledonia, it spent 26% of its time inspecting a large number of fish (59.5 +/- 5.1 per 15 minute) (Grutter 1999).

It consumes a large number of parasites (1218 +/- 118) each day or 4.8 +/- 0.4 parasites per minute (Grutter 1996) and most of the prey items were juvenile gnathiid isopods (Grutter 1997). The biomass of gnathiids in the diet in New Caledonia was lower than at Lizard Island, but higher than at Heron Island, suggesting that the role of gnathiids in cleaning behaviour is variable (Grutter 1999).

At One Tree Lagoon on the Great Barrier Reef, overall mortality during first year for L. dimidiatus was 50%, juveniles do not shelter within the substratum and displayed relatively high mortality over the first twelve months (Eckert 1987). The average annual mortality ofL. dimidiatus was 11.1 +/- 2.2 %.

This species is heavily targeted for the aquarium trade, especially for its cleaning behaviour (Kuwamura 1976).

In Sri Lanka, about 20,000 individuals were exported annually, it is considered as a top export species in the marine ornamental trade (Wood and Rajasuriya 1999, Ekaratne 2000, Wood 2001). Due to its ‘cleaning service’ behaviour, there are concerns at the high aquarium trade for L. dimidiatus and other Labroides species, which may have negative impacts on the health of other reef fishes (Edward and Shepherd 1992).

There are no specific conservation measures in place for this species. Its distribution overlaps several marine protected areas within its range.

This species has been observed at protected areas on the Great Barrier Reef, Australia (Hutchins and Sawinston 1996), at Ras Mohammed National Park, Egypt (Bshary 2003) and in the Mafia Island Marine Park, Tanzania (Garpe and Öhman 2003). Given the intensive collection of this species for the aquarium trade, more research is needed on the local and global impact of collection, as well as on the implementation of sustainable harvest and trade measures.